In-the-mold coating apparatus and method

ABSTRACT

A method and apparatus for forming a thermoset in-the-mold coating on a hot, cured glass fiber reinforced thermoset resin substrate by (1) separating the mold halves slightly while maintaining a seal with the shear edge, (2) injecting an in-the-mold coating resin in a stream which flows parallel from the injector onto a surface of the substrate, and (3) closing the mold and curing the coating under pressure. The separation and of the mold halves is performed by the conventional mold ram. Preferably the mold surface forming the coated surface of the substrate is roughened.

This application is a division of application Ser. No. 974,583, filedDec. 29, 1978 now U.S. Pat. No. 4,235,833 issued Nov. 25, 1980 which inturn is a Continuation-In-Part of Ser. No. 944,093 filed Sept. 20, 1978,which in turn is a Continuation-In-Part of Ser. No. 897,980 filed Apr.20, 1978, now abandoned which in turn is a Continuation-In-Part of Ser.No. 814,502 filed July 11, 1977 now abandoned.

The parent and grandparent applications are directed to the in-the-moldcoating compositions and related processes during curing. In-the-moldcoating processes involve, first molding a base portion of the articlein the cavity of a pair of relatively movable die members of a diemolding set. The base portion of the article is allowed to cure afterwhich a skin forming coating material is injected onto the surface to beimproved. Pressure is applied onto the die members so as to distributethe skin forming coating material substantially uniformly across thesurface of the base portion and thereby substantially fill the porosityand any shrink portions on the surface. The prior art is best set forthin U.S. Pat. Nos. 4,076,780; 4,076,788 and 4,082,426, all assigned toGeneral Motors and an article entitled, "The Mechanics for MoldedCoating for Compression Molded Reinforced Plastic Parts" by RobertOngena, 33rd Annual Technical Conference, 1978, ReinforcedPlastics/Composites Institute, The Society of the Plastics Industry,Inc., Section 14B, pages 1-7, and Modern Plastics, June 1976, pages54-56 by William Todd.

The apparatus disclosed in the prior art consists of a pair ofrelatively movable die members, one of which is movable towards theother through a hydraulic ram. When the die members are closed, a cavityis formed therebetween for molding an article in a desiredconfiguration. One of the die members is characterized in that a chamberis formed therein which communicates with the cavity and is adapted toreceive a metered amount of liquid coating material in the form of athermosetting resin which is subsequently used for coating one surfaceof the molded article. The chamber is provided with a slidable piston orplunger which is movable through an appropriate actuator so as todisplace the liquid coating material from the chamber into the cavityand onto one surface of the molded article without requiring the diemembers to be opened. The coating material is applied to the chamber byan injector device which has a body portion, one end of which is formedwith a nozzle that is located adjacent to the chamber. The nozzle isselectively movable into and out of sealing engagement with an inletport formed in the associated die members and communicating with thechamber. When the base portion of the article is first being molded inthe cavity, the piston in the chamber is flush with the mold cavity andso positioned that both the chamber and the inlet port are closed fromcommunication with the cavity. After the base portion of the article ishardened sufficiently to retain its shape, the piston is moved by theactuator to a second position exposing a predetermined volume of thechamber to the cavity. Simultaneously, the injector device is moved intothe inlet port and the liquid coating material is supplied to thechamber with the hydraulic pressure on the ram being relieved. With thenozzle of the injector positioned in the inlet port, the piston is movedby the actuator towards the cavity so as to force the coating materialunder pressure onto the surface to be coated. The press ram is againactuated to cause the die members to move toward each other and applypressure to the coating material and the pressure and temperature ismaintained for a time sufficient for the coating material to set upsufficiently to allow opening of the die members and ejection of thecoated molded article.

The prior art mold dies are maintained in a parallel configuration byhydraulic cylinders mounted on the bottom press plates pushing upwardagainst the upper plate. The cylinders also part the dies for injection.A fifteen hundred ton ram forces the upper plates downward resulting intwo hydraulics operating against each other. The apparatus of the priorart, through a significant advance in the art, is extremely complexinvolving a toggled nozzle which comes into contact with the mold, fillsa reservoir then retracts, then the contents of the reservoir areinjected into the mold.

The present invention eliminates the need for the toggle mechanism, thereservoir, the reservoir fluid ejector system and the prior arthydraulic leveling system.

The present invention is directed to a process and apparatus including awater cooled valved injector nozzle which is permanently mounted in ahot die member. The injector nozzle injects directly into the moldcavity. A stream is injected parallel to a roughened substrate surface.The die forming the roughened surface has, in turn, a rough surface.Mechanical assists on the corners of the movable upper die need not beused to supplement the lifting force created by the hydraulic fluid usedto open the mold. Conventional heel blocks are used to maintain the diesin a parallel configuration. In addition, appropriate controls need notbe employed to synchronize with the opening of the mold or with the rateof flow of the coating material into the cavity.

One way of carrying out the invention is described in detail below withreferences to the drawings in which,

FIG. 1 is a view partially in section of a mold having the valvedinjection nozzle mounted in the lower die thereof.

FIG. 1a is a view partially in section of the valved injection nozzle.

FIG. 2 is a view of the Teflon baffel used in the injection nozzle ofFIG. 1.

FIG. 3 is a figure of the dies showing pillow blocks.

FIG. 4 is a top view of the bottom die showing a roughened surface.

Referring to the drawings, a conventional hydraulic press, not shown,supports a pair of relatively movable die members 2 and 4, the lowerone, of which identified by reference numeral 2, is rigidly secured tothe base while the upper die member 4 is fixedly connected with a platemember which, in turn is movable vertically through a double actinghydraulic ram mounted on the support member. The hydraulic ram serves toraise the upper die member 4 relative to the lower die member 2, and,although not shown, the upper die member 4 is guided during suchmovement through appropriate guide members. Thus, by actuating thehydraulic ram, the upper die member 2 can assume an open raised positionor a lowered close position as shown in FIG. 1. When the die members 2and 4 are closed, they form a cavity for molding a plastic article underheat and pressure in a desired configuration. The die members 2 and 4cannot only serve to mold a plastic article as seen in FIG. 1, but, inaddition, the die member 2 incorporates parts and components to bedescribed hereinafter that provide a coating on one surface of themolded article. The coating is in the form of a liquid skin formingthermosetting resin which is injected against the surface being coated.

In order to deliver the liquid thermosetting resin coating material tothe surface to be improved, the lower die member 2 has been designed soas to include a valved injector nozzle 6. In this regard, the lower diemember 2 is formed with a horizontally oriented cylindrical recess 8 inwhich valved injector nozzle 6 is permanently mounted. Valve pin 10 isconnected to an actuator in the form of a double acting hydraulic piston12 movable in cylinder 14. By directing pressurized fluid to one end orthe other of the hydraulic cylinder 14, the piston 12 is movable betweenthe fabric bumper 16 and fabric bumper 18. Movement of the piston 12 tofabric bumper 18 opens injector valve 20. In the open position,thermosetting resin 22 flows through material inlet 24, stainless steelbarrel 26 through open valve 20 and into the mold cavity 28.

The injector device 6 is carried by the lower die member 2, and as seenin FIG. 1, includes a cylindrical recess 8 having its end portion 30threaded, which serves to securely mount the injector device to thelower die member 2 by threaded nozzle end 32. The outer sleeve member 34is secured at its left-hand end as seen in FIG. 1 to an elongated innerbarrel 26 through flange 34 at its righthand end, the outer sleevemember 34 is attached to barrel 26 through the injector nozzle assembly36. The inner periphery surface of a portion of the sleeve member 34,together with the outer surface of barrel 26, form passages for coolingfluid to be directed from inlet 38 around the barrel 26 and then exhaustat outlet port 40. Teflon baffels 42 are positioned in the coolingpassage to direct the flow of cooling water to the cooling chamber 43 ofinjector nozzle assembly 36. As seen in FIG. 2, Teflon baffel 42 hasflat surfaces 44 and 45 which permits water to flow between the outersleeve member 34 and the Teflon baffel 42 and enter the injector nozzleassembly 36. This barrel 26 fits through hole 46. Directing cooling ofthe water to the injector nozzle assembly 36 keeps the injector nozzleassembly cool enough that it does not cause the resin injected by thenozzle to cure, but warm enough so that it doesn't cool the part of themold to which it is attached and cause undercure of resin in that area.

The valved nozzle is opened and closed by air at 100 psi (689 KPa) orhydraulic fluid at 1,000 psi (6894 KPa) when hydraulic fluid (includingair) is directed via a port 48 in flange 34, to the chamber at theleft-hand side of the piston member 12, the pin 10 is shifted towardsthe left allowing resin to be injected into the mold. On the other hand,when hydraulic fluid is directed via a port 50 in flange 52 to thechamber at the left side of piston member 12, the pin 10 of the injectordevice moves to the right closing the valve at 20 and pin 10, completingthe smooth surface on the inside of die 2.

Air is the preferred fluid as it eliminates the danger of contaminatingthe injector resin with hydraulic fluid. The injector resin ismaintained at 1,000 psi (6894 KPa) so that any leakage will be resininto the air chamber and not vice-versa.

The in-the-mold coating resin is fed into the valved injector at resininlet 54, which is adapted to be connected through a conduit (not shown)to a source of pressure supplied ingredients which make up one or a twocomponent thermosetting resin system. If a two component resin is used,a static mixer such as that made by Kenics Corporation serves to mix thetwo liquid components of the thermosetting resin system prior tointroduction through port 24.

Other known mixers can also be used. It should be apparent that when thepin 10 is moved toward the left, the nozzle will be opened and permitthe thermosetting resin coating material to flow into the upper diemember 2 if the pressure is great enough to overcome the pressureexerted by the press on the die. The lower die 2 has a roughened innersurface 3. This imparts a roughened surface to the substrate part. Flowof in-the-mold coating resin across the roughened surface causes aseparation of resin and filler, leaving a resin-rich layer on thesubstrate surface. The resin-rich layer appears to aid adhesion. Theindentations in the surface of the die can range from about 0.001 mm to0.01 mm.

The apparatus described above operates as follows. Initially the upperdie member 4 is raised relative to the lower die member 2 so as toexpose the cavity portion within the lower die member. Slabs of sheetmolding compound are then placed in the bottom of the lower die member 2within the cavity at appropriate locations. Pin 10 is positioned to forma smooth inner surface with the inner surface of die 2 by pressurizationof port 50. The mold is pressurized, driving the heated upper die member4 downwardly into telescoping engagement with the fixed heated lower diemember 2. As the upper die member 4 closes on the lower die member 2,the slabs of sheet molding compound are deformed under heat and pressureand flows to fill the mold cavity and any rib forming grooves therein soas to form a ribbed substrate and is identified by the reference numeral28. The molding pressure generated by the ram of the mold is maintainedon the upper die member 18 until the substrate 28 cures and hardenssufficiently to permit separation of the upper die member 4 withoutadversely affecting the substrate. Mold timer No. 1 is set at 1/2 to 5minutes to accomplish the initial cure.

During the cure cycle, sink marks are usually formed above the ribs dueto shrinkage occurring. Similarly, the surface of the substrate may alsohave other imperfections, such as porosity, line cracks, etc. Suchdefects in the outer surface of the substrate 28 are eliminated byproviding a cosmetic coating to the surface to be improved. This coatingis applied, according to this invention, during the final stages ofcuring of the substrate.

In applying the coating, the ram pressure of the mold initially isrelieved on the upper die member 4 by operation of a timer T-2, which isset at about 1 to 4 seconds. This opens the mold 1/2 inch. Pressurizedfluid is directed through port 48 to the left side of the piston member12 while the other side of the piston member is vented via port 50. Thedegas timer T-3 of the mold is used to control both the movement of pin10 and the mold opening time. In-the-mold coating material is injectedfor about 1 to 15 seconds through material inlet port 24. When T-3 hastimed out, the press comes back down to tonnage and is timed out by T-4(about 1 to 15 minutes) to cure the coating. Simultaneously with thepress coming down, pin 10 is moved back to form part of the inner moldwall.

During the time that the pin 10 is retracted, the coating material flowsinto the cavity. The coating material moves outwardly parallel to thesurface of the substrate 28 hydraulically pressing the latter tightlyagainst the upper die member 4 and thereby preventing its dislodgementor unseating therefrom. Following the pressurized supply of the coatingmaterial onto the lower surface of the substrate 28, the press is onceagain activated so as to close the die members 2 and 4 and cause thecoating material to be uniformly distributed on the surface to becoated. Heel blocks 60 which mate with recesses 62 align the dies of theclosing mold. Guide pins and mating recesses can also be used inconjunction with the heel blocks. The pressures and temperatures as wellas the type of coating material that can be utilized with the apparatusaccording to this invention is fully described in the aforementionedparent and grandparent patent applications. Accordingly, attention isdirected to the parent applications for a full understanding of theprocess that can be practiced with this invention.

Specific examples for injecting the coating by using an injection nozzlewhich has a pin protruding through the opening in the nozzle will now beset forth. In the closed position the end of the pin forms a smallportion of the inner mold surface. In the open position, the pin ispulled back from the mold and from the opening in the nozzle allowingcoating material to be injected into the mold. The pin is stabilizedagainst rotation so that it will always form a smooth surface with themold wall in the closed position. The nozzle is at a differenttemperature from the mold because it is water cooled.

Charge weights giving as much as 0.5 mm of coating have been used, butan average of 0.07 to 0.10 mm of coating has generally been enough togive both opacity and complete coverage. Since the usual substrate partaverages 2.5 mm in thickness, a typical coating has required about 0.03to 0.05 gm of coating per gm of SMC (sheet molding compound) used.

Simple coating charge placements, often a single pool or strip formed byhigh pressure injection usually have provided complete coverage.

Mold temperatures from 140° to 160° C. have given satisfactory coatings.A minimum cure time of 10 to 30 seconds at 150° C. has been used butslower cure rates have sometimes been required to prevent too rapidgelation resulting in incomplete coverage.

Higher molding pressures, as expected, provide better coverage ofsteeper, lower draft surfaces. However, the typical pressures needed tomold the base SMC part have also generally been adequate to give acomplete coating. The principle aim of the in-the-mold coating has beento fill voids, reduce sinks and act as a replacement for theprimer-sealer now commonly used by custom molders of SMC.

In-the-mold coated parts have passed the automotive tests normally used.

In the following examples as elsewhere in the specification and claims,all parts and percentages are by weight unless otherwise specified.

EXAMPLE I

A 1973 Oldsmobile grill opening panel was molded using a standard Rohm &Haas unsaturated polyester based sheet molding compound using 68.95 KPapressure (1,000 psi). The press used was manufactured by Erie Press inErie, Pa. Most of the presses made by the various manufacturers haveautomatic degas controls or they can be added.

The automatic degas cycle of the press was activated to control thesequence necessary for molding the parts, opening the mold to inject thein-the-mold coat and reclose on the proper pressure to coat the parts.The parts were molded and were excellent in appearance. They were testedand passed all the tests run. The coating, in some instances, was sothick that a cross-hatch adhesive could not be run. The one componentin-the-mold coating was 2.2 mm thick. The molding sequence was asfollows.

All four timers on press were used. Timer No. 1 (T-1) is the precuretimer and was set at 21/2 minutes to mold and cure the part. When thecure time has elapsed and the press comes off tonnage T-2 times the flowof oil to return the ram (set at 1-11/12 seconds), this opens the moldto 13 mm.

In-the-mold coating material was then injected into the mold with thetimer on the injector being the T-3 time, which, in this case, was setat 13 seconds. When T-3 has timed out, the press came back down and ontotonnage and was timed out by T-4 (60 seconds) to cure the coating.

This whole sequence worked very well for molding and coating parts andthe press repeated the same sequence correctly every time except T-2which appeared to result in a 3 mm variation either way once in a while.This is understandable as break-away force needed can and will fluctuatewith fluctuation in charge weight and charge placement when shears areas wide open as on this part.

With this set-up, precure pressure and cure pressure were different tohide sinks over bosses and ribs. Mold cure pressure was reduced to78,740 Kg/area of front end (100 tons/area front end) less than precuretonnage to reduce the tendency for parts to crack.

An interface signal from T-2 is used to activate the injector andanother signal from T-3 is used to shut it off. This eliminates a needfor a separate timer for the injector. During injection a seal wasmaintained by the shear edge of the mold. The following in-the-moldcoating composition was the one injected through a cooled injectionnozzle positioned between the parting surfaces of the mold and injectingparallel to the parting surfaces.

The coating composition used had the following formulation.

    ______________________________________                                        Components             Parts                                                  ______________________________________                                        Vinyl ester resin.sup.1 in styrene (be-                                        lieved to be 66% copolymer of                                                 acrylic acid and diglycidyl ether                                             of bisphenol A in 44% styrene                                                 some trimethoxyphenol is present                                              for cross-linking)    200                                                    40% polyvinyl acetate, free of car-                                            boxyl groups, dissolved in 60%                                                styrene.sup.2         80                                                     Styrene                40                                                     Canadian talc 0.03mm average par-                                              ticle length          200                                                    Suzorite mica (phlogopite) 0.03mm                                              average particle length                                                                             140                                                    Tertiary butyl benzoate                                                                              6                                                      Saturated solution of parabenzo-                                               quinone in styrene (inhibitor)                                                                      0.6                                                    Dialkyl phosphate.sup.3 (mold release)                                                               3.0                                                    ______________________________________                                         .sup.1 Dow XD 9013.02                                                         .sup.2 Union Carbide LP90                                                     .sup.3 Zelac NE duPont                                                   

The following are the processing parameters and test results of ExampleI:

    ______________________________________                                        Mold temperature 295° F.                                               SMC Cure Time    2 mins.                                                      Coating Cure Time                                                                              1 min.                                                       Coating Thickness                                                                              3 to 18 mils (18 mils on hori-                                                 zontal uniform)                                             ______________________________________                                    

The parts are presently being evaluated in actual handling and use. Nofailures have been reported.

EXAMPLE II

Example I was repeated manufacturing test parts using a two componentin-the-mold coating composition. The formulation is generally set forthin U.S. Pat. No. 4,081,578. A proportioning pump was used. The pump hastwo large cylinders. The piston in each cylinder was driven by a commondrive so that each piston moved exactly the same distance. One cylindercontained one reactive component and the other cylinder contained theother reactive component. The displacement of the two cylinders is morethan sufficient for one in-the-mold coating. The output from the twocylinders was mixed in a static mixer (Kinex Mixer) and injected intothe mold using the valved injector nozzle of the present invention. Thecure time for the in-the-mold coating was one minute.

Other than the above recited differences, the same procedure wasfollowed as that set forth in Example I.

The preferred mold has a chrome or nickel-plated cavity. The interiorfaces of the mold are preferably roughened by impingement with glassbeads or sand-blasted prior to chrome plating. The roughened surfacecauses a separation of the resin and filler of the in-the-mold coatinggiving a resin-rich phase at the interface between the substrate and thein-the-mold coating.

Both the injector and the proportioning pump are available from theTompkins-Johnson Co., 2425 West Michigan Ave., Jackson, Mich. 49202.

Various changes and modifications can be made in this constructionwithout departing from the spirit of the invention. Such changes andmodifications are contemplated by the inventors and they do not wish tobe limited except by the scope of the appended claims.

We claim:
 1. In an apparatus for forming a glass fiber reinforcedthermoset resin part having(a) a mold having a lower die (2) and anupper die (4) and a ram for opening and closing the mold; (b) a meansfor parting one of the mold dies from the part while maintaining themold sealed, in a timed sequence after the part is cured; (c) a timer tocontrol the timed sequence; (d) an injector (6) having a water cooledinjection nozzle permanently attached to one of the two dies for thepurpose of injecting a coating resin upon the glass fiber reinforcedresin part formed between the two dies only during the parting; (e) themeans to control the timed sequence consisting of the timer of the moldused to control the molding cycle;wherein the improvement comprises (f)the injector being positioned in the die so that a stream which flowsfrom the injector flows parallel from the injector onto the surface ofthe part; (g) the parting means consisting of the ram which forces themold closed; (h) the means to control the timed sequence of the moldparting step consisting of the timer of the mold used to control thedegass cycle; and (i) wherein a roughened surface on the die is thesurface of the die which forms the more visible surface of the part.